In a Ziploc bag, combine minced garlic, lemon juice, white wine vinegar, extra virgin olive oil, dried oregano, ground mustard, and kosher salt. Add the chicken breasts, seal the bag, and massage the marinade into the chicken. Let it marinate in the refrigerator for at least 1 hour or overnight for best flavor.

Bring a small pot of water to a boil and blanch thinly sliced red onions for 10 seconds before draining. In a separate bowl, heat apple cider vinegar and sugar until dissolved. Pour this mixture over the drained onions to cool for about 20 minutes.

Grate an English cucumber and drain to remove excess moisture. In a bowl, combine the drained cucumber with minced garlic, lemon juice, white wine vinegar, olive oil, Greek yogurt, kosher salt, and pepper. Stir and let sit for at least 20 minutes.

Preheat a grill or skillet over medium-high heat. Remove the marinated chicken and cook for 5-6 minutes on each side until it reaches 165°F and is browned. Let rest for a few minutes before slicing into strips.

Divide cooked quinoa among bowls. Top with sliced chicken, pickled onions, halved grape tomatoes, and fresh cucumber. Crumble feta cheese on top, drizzle with tzatziki, and finish with parsley and mint.